diff --git a/crates/copilot_chat/src/copilot_chat.rs b/crates/copilot_chat/src/copilot_chat.rs
index 513b813517cc7f929f922842611f78fb617ff396..86247bce793b136f189854599f5c9ef57c5fe0c5 100644
--- a/crates/copilot_chat/src/copilot_chat.rs
+++ b/crates/copilot_chat/src/copilot_chat.rs
@@ -223,7 +223,7 @@ impl Model {
     }
 
     pub fn max_token_count(&self) -> u64 {
-        self.capabilities.limits.max_prompt_tokens
+        self.capabilities.limits.max_context_window_tokens as u64
     }
 
     pub fn supports_tools(&self) -> bool {
@@ -1038,6 +1038,61 @@ mod tests {
         assert_eq!(schema.data[0].vendor, ModelVendor::Unknown);
     }
 
+    #[test]
+    fn test_max_token_count_returns_context_window_not_prompt_tokens() {
+        let json = r#"{
+              "data": [
+                {
+                  "billing": { "is_premium": true, "multiplier": 1 },
+                  "capabilities": {
+                    "family": "claude-sonnet-4",
+                    "limits": { "max_context_window_tokens": 200000, "max_output_tokens": 16384, "max_prompt_tokens": 90000 },
+                    "object": "model_capabilities",
+                    "supports": { "streaming": true, "tool_calls": true },
+                    "type": "chat"
+                  },
+                  "id": "claude-sonnet-4",
+                  "is_chat_default": false,
+                  "is_chat_fallback": false,
+                  "model_picker_enabled": true,
+                  "name": "Claude Sonnet 4",
+                  "object": "model",
+                  "preview": false,
+                  "vendor": "Anthropic",
+                  "version": "claude-sonnet-4"
+                },
+                {
+                  "billing": { "is_premium": false, "multiplier": 1 },
+                  "capabilities": {
+                    "family": "gpt-4o",
+                    "limits": { "max_context_window_tokens": 128000, "max_output_tokens": 16384, "max_prompt_tokens": 110000 },
+                    "object": "model_capabilities",
+                    "supports": { "streaming": true, "tool_calls": true },
+                    "type": "chat"
+                  },
+                  "id": "gpt-4o",
+                  "is_chat_default": true,
+                  "is_chat_fallback": false,
+                  "model_picker_enabled": true,
+                  "name": "GPT-4o",
+                  "object": "model",
+                  "preview": false,
+                  "vendor": "Azure OpenAI",
+                  "version": "gpt-4o"
+                }
+              ],
+              "object": "list"
+            }"#;
+
+        let schema: ModelSchema = serde_json::from_str(json).unwrap();
+
+        // max_token_count() should return context window (200000), not prompt tokens (90000)
+        assert_eq!(schema.data[0].max_token_count(), 200000);
+
+        // GPT-4o should return 128000 (context window), not 110000 (prompt tokens)
+        assert_eq!(schema.data[1].max_token_count(), 128000);
+    }
+
     #[test]
     fn test_models_with_pending_policy_deserialize() {
         // This test verifies that models with policy states other than "enabled"